The objective of the research is to examine the role of response error (trait desirability, need for social approval, response acquiescence) in field studies of the prevalence of psychiatric impairment. Data will be acquired by household interview using a stratified sample (N equals 1,350) with optimal allocation by socioeconomic status and ethnicity. The sampling frame to be used is the almost 8,000 respondents interviewed in 1974 in Alameda County, California by the Human Population Laboratory for Epidemiologic Studies. Ethnicity is defined using ethnic heritage, e.g., Blacks, Mexican American, and Anglos. Response tendencies will be studied in relation to two psychiatric screening instruments: the Center for Epidemiologic Studies Depression Scale (CES-D) and the Psychiatric Epidemiology Research Interview (PERI). Data analysis will focus on the magnitude and direction of error introduced by response tendencies in contrasting sex, socioeconomic status, and ethnic groups. For example, how much variance in symptom scores are attributable to response tendencies as compared to sex, socioeconomic status, and ethnicity. A second focus is on the effects of response bias on the sensitivity/specificity of the CES-D and the PERI in contrasting ethnic, sex, age, and income groups. One-two weeks after being interviewed initially by lay interviewers, respondents will be re-interviewed by clinical psychologists using the Schedule for Affective Disorders and Schizophrenia.